With oil skimmers utilizing endless belts, typically, the belt is suspended from a driven head pulley. The belt is also passed around a tail pulley that is positioned in a body of water. When the head pulley is rotatably driven, a descending reach of the belt on entering the body of water will pick up surface oil and carry that oil around the tail pulley to an ascending reach of the belt. Wipers are positioned below of the head pulley near the top of the descending reach to scrape oil from the surface of the belt. Collection pans positioned below the wipers receive the separated oil and deliver the separated oil to a collection vessel for recycling or appropriate disposal.
In the past, the tail pulleys have usually either been mounted in a vessel containing the oil and water to be separated or alternately, supported exclusively by the belt. As an example of the latter, if oil is to be removed from a contaminated water well, an elongated belt supporting a tail pulley is dropped into the well, and the weight of the pulley and the belt provide belt tension. Clearly, if the belt breaks, there is a problem because the pulley will be dropped into the well and either lost or, at best, retrievable only through a successful "fishing" operation. Even if the belt does not break, on occasion, a pulley will slip out of the belt as the belt is lowered or during operation, and once again, an operator has, at best, a difficult retrieval process to confront.
Where tail pulleys are rotatably mounted in tanks, as an example, other problems manifest themselves. If the axes of rotation of the head and tail pulleys are not precisely parallel, the belt will not track properly and excessive wear can occur. If the belt is steel, the wear is exacerbated and considerable damage can be caused to both the belt and either or both of the pulleys. Another problem is that it is difficult to obtain and maintain proper belt tension. Here again, the problem is exacerbated if the belt is steel. If a piece of debris gets caught between the belt and the tensioned bottom pulley, the belt will inevitably become damaged due to excessive tension. Further, if the head pulley is equipped with magnets to drive the belt, a malaligned or protruding magnet can cause excessive belt tension that results in belt failure.
Attempts have been made to provide portable oil skimmers which may be transported from place to place as a unit so that the unit may be installed as needed at remote locations. These attempts have all suffered shortcomings, primarily due to the belt tracking and breakage problems.
Another problem is that when endless belt oil skimmers are used in quiescent bodies of water, their efficiencies can be relatively poor. The relatively poor efficiency is due to the fact that the belt picks up oil as it enters a water body and if the body is quiescent, the surface in the vicinity of belt entry soon becomes relatively oil free. Further, pick-up must wait for a relatively slow migration of oil from portions of the body surface remote from the belt entry location.